As is well known, the rear suspension system of a vehicle typically includes a plurality of control links. In many cases, these control links attach an axle to the frame or chassis of the vehicle to restrain fore, aft, and lateral motion of the axle relative to the vehicle frame. These control links may be arranged in any number of configurations depending upon the specific vehicle support structure used and the operating conditions of the vehicle to stabilize the forces acting on the axle. For example, three-link and five-link systems have been used in vehicles having a frame-type construction, such as trucks and sport-utility vehicles.
The five-link rear suspension system comprises four longitudinal control links and one transversal control link, or trackbar, pivotally connecting the axle to the frame of the vehicle. The four longitudinal control links are typically attached at one end to the axle and at the other end to the frame of the vehicle. These four longitudinal control links stabilize only fore and aft motion of the axle. The single trackbar is typically attached at one end to the carrier or differential assembly and at the other end to the frame of the vehicle. The trackbar, thus, stabilizes only lateral motion of the axle.
The five-link system has the distinct disadvantage of forcing a lateral shift in the axle position as the vehicle suspension travels up and down. This lateral shift is transmitted to the passenger compartment of the vehicle and produces an objectionable "head toss" response of the passengers. This phenomenon is more pronounced when the vehicle is towing a trailer. Such lateral shift in the axle position produces an orbital yaw in both the trailer and the vehicle, thereby producing objectionable trailer response.
Furthermore, the five-link system has the additional disadvantage of requiring the trackbar orientation to be dependent on whether the vehicle is right-hand drive or left-hand drive. That it, if a vehicle is produced for sale in the United States, the front five-link suspension is configured for left-hand drive. Consequently, the trackbar orientation in the rear suspension must be oriented to counteract the forces in the front suspension. If the same vehicle is produced for sale abroad, the front five-link suspension is configured for right-hand drive. Consequently, the trackbar orientation in the rear suspension is oriented opposite that of the left-hand drive configuration. Such change in the rear suspension design increases the cost of producing vehicles for worldwide sale.
In an attempt to overcome the disadvantages of the five-link suspension system, a three-link system has been developed. The three-link system comprises a pair of longitudinal control links pivotally connecting the axle to the frame of the vehicle. The pair of longitudinal control links is typically attached at one end to the axle and at the other end to the frame of the vehicle. These longitudinal control links stabilize only fore and aft motion of the axle. A generally triangularly shaped control link, or A-arm, is also provided for stabilizing the lateral motion and further stabilizing the fore and aft motion of the axle. The A-arm is also pivotally connected to the frame on its ends and pivotally connected to the axle at its central portion.
The three-link system has the advantage of minimizing the lateral shift of the axle, thereby minimizing the "head toss" response of the passengers. Such minimization of the lateral shift further improves the ride comfort and vehicle control when the vehicle is towing a trailer. Moreover, the three-link system utilizes the same design for both left-hand drive and right-hand drive vehicle configurations. Consequently, the manufacturing cost of producing vehicles for multiple worldwide markets can be greatly reduced. The three-link system further reduces the number of vehicle parts and attachment points to reduce the cost of manufacturing.
The three-link rear suspension system has been incorporated into frame-type vehicles with various degrees of success. Some known designs utilize a pair of horizontally disposed bushings. These horizontally disposed bushings are pivotally interconnecting the ends of the A-arm to the frame of the vehicle. Specifically, these horizontally disposed bushings are attached to a vehicle cross-member with clevis attachments. The purpose of the vehicle cross-member is to provide structural support for transferring loads from the vehicle suspension system to the frame and, further, to provide a dimensionally acceptable mounting support for receiving the bushing attachments. However, it should be noted that the structural cross member is assembled to the frame of the vehicle only after the bushing brackets are mounted on the cross member.
A disadvantage of these horizontally disposed bushings is that they may not provide an optimal connection of the suspension system to the vehicle. Specifically, due to the horizontal orientation of the bushings, sufficient lateral stiffness may not be achieved without the use of additional external compressive restraints, such as rubber bumpers. It should be appreciated that such additional compressive restraints increase the cost and difficulty of assembling the suspension system. Moreover, in a preferred suspension design the fore/aft bushing rate and vertical bushing rate are generally identical and comparably larger than the axial or lateral rates. It is believed that this preferred rate relationship provides improved ride and handling characteristics in the vehicle. However, in the horizontally disposed bushing configuration, the actual bushing rate relationship is opposite to the preferred rate relationship, thereby failing to provide an optimal configuration.
In the case of a unit-body construction vehicle, three-link suspension systems are not readily implemented. Unit-body vehicles, or "Uni-body" vehicles, differ from frame-type vehicles in that the uni-body vehicle, unlike frame-type vehicles, has no discernible frame. The structural integrity of the uni-body design is achieved through the body itself using a pair of opposing, longitudinally extending sills. The structural integrity of frame-type design is achieved through a frame member generally extending the length of the vehicle. The frame, in turn, carries the major components of the vehicle, such as the engine, suspension, and body.
Due to the lack of structural cross members in an uni-body vehicle, attachment of the A-arm of the three-link system is more difficult. In fact, the cross-vehicle tolerances for the sill members prohibit the use of horizontally disposed bushings unless a separately attached cross member is used for receiving the bushing attachments. By way of example, these cross-vehicle tolerances for the sill members may be several millimeters. However, this separately attached cross member, when used in an uni-body application, is considered a sub-frame. The addition of a sub-frame increases the cost and assembling difficulty of the vehicle.
Accordingly, there exists a need in the relevant art to provide a three-link rear suspension system capable of maximizing the lateral stiffness of the rear suspension system. Furthermore, there exists a need in the relevant art to provide a three-link rear suspension system capable of being coupled to an uni-body vehicle without the use of a sub-frame, which overcomes the above disadvantages.